(a) Field of the Invention
The present invention generally relates to a system and method for transmitting and receiving wideband speech signals.
(b) Description of the Related Art
A wideband speech signal has a frequency of 0˜8 kHz, which is twice that of a currently used telephone-line band, at 0˜4 kHz. The wideband speech signal is suitable for a next-generation speech communication system because it is less artificial than a signal of the telephone-line band, and has high intelligibility.
The G.711 is one of the methods of digitalizing and compressing a speech signal of the telephone-line band, which has been standardized by ITU-T (International Telecommunication Union-Telecommunication Standardization sector) for the first time. G.711 uses nonlinear pulse code modulation (u/A-PCM), and it is known that its performance is similar to the original speech signal at 64 kbit/s. Other speech compression methods standardized by ITU-T include G.726 (adaptive differential pulse code modulation, ADPCM, 32 kbit/s), G.728 (low delay code excited linear prediction, LD-CELP, 16 kbit/s), G.729 (conjugate structure algebraic code excited linear prediction, CS-ACELP, 8 kbit/s), and G.723.1 (ACELP/MP-MLQ, 5.3/6.3 kbit/s).
Among ITU-T standard speech coders, G.723.1 and G.729 were adopted as a VoIP (Voice over Internet Protocol) standard coder on the Internet. G.723.1, developed for the purpose of compressing multimedia signals at a low rate, is an algorithm capable of compressing and decompressing input speech at two bit rates of 5.3 kbit/s and 6.3 kbit/s. G.723.1 uses the analysis-by-synthesis method, which has the widest application field among speech coding methods, and provides toll quality as high as that of a wired network. ITU-T G.729 is an algorithm capable of compressing and decompressing input speech at the rate of 8 kbit/s using an algebraic codebook, and it also provides toll quality as high as that of the wired network. Furthermore, ITU-T G.729A (G.729 Annex A) has the same transmission parameter as that of G.729 so it has compatibility with G.729 and it has advantages in complexity. Accordingly, G.729A is widely used in actual systems.
The above-described speech coding methods or systems with low transmission rates that provide toll quality as high as that of wired networks have created new services in mobile communications and Internet phone services. In particular, VoIP on the Internet is being spread very rapidly due to inexpensive telephone charges. However, the aforementioned conventional coding methods or systems have had poor service quality because of low quality and long delay time caused by packet loss on the Internet. With the development of communication networks and protocols, however, most of the problems in the conventional coding methods or systems with respect to delay time generated on networks have been solved. Recently, attempts to extend a speech signal to a wideband signal having a frequency (0˜8 kHz) twice that of telephone-line band (0˜4 kHz) to improve toll quality have been made. However, the 16 kHz wideband speech codec, which has been already standardized, has no backward compatibility with the telephone-line band codec currently being used for VoIP services so a new communication system must be designed in order to use signals of the two different systems. Furthermore, since the wideband signal occupies a wide bandwidth, a network capable of processing a large amount of data is needed. Accordingly, there are many problems in providing new services with the current systems.